Coated paper duplicating master



061;. 31, 1967 M, {)FQT 3,349,7Wi

COATED PAPER DUPLICATING MASTER Filed Jan. 28, 3.965

EGO Z x I ig FIG, 2 Q) lNVENTO George M Ort United States Patent 3,349,704 COATED PAPER DUPLICATIN G MASTER George M. Ort, Chicago, 111., assignor to A. B. Dick Company, Niles, lll., a corporation of Illinois Filed Jan. 28, 1965, Sol. No. 428,815 5 Claims. (Cl. 101-461) This invention relates to duplicating masters formed of coated paper and relates more particularly to coated paper masters of the type adapted to be imaged by processes which include heat to form or set the image on the coating.

Typical of the processes in which heat is employed to set an image is the electrostatic process referred to commercially as the Electrofax process or the Xerox process. In the Electrofax process, the latent electrostatic image is formed directly on a lithographic surface of a coated paper lithographic plate. The image is developed by toning with a developing powder formulated of an ink receptive, water repellent imaging material. The image is then set on the lithographic surface by the application of heat to fuse the powder and form the ink receptive image on the coated surface of the lithographic plate. In the Xerox process, the latent electrostatic image is formed on a photo-conductive plate and developed by the developing material or powder which is transferred from the plate to the coated surface of the coated paper lithographic plate. The latter is then heated to fuse the developing material and set the ink receptive, water repellent image on the lithographic, ink repellent, water receptive surface.

Heat is employed also in the development of an image in the thermographic process wherein a coated master is brought into surface contact with a transfer sheet provided with a heat pattern which may be formed by infrared radiation of an original in which the imaged portions contain an infrared ray absorbing, heat-generating material. The image is formed indirectly by transfer of ink receptive, water repellent imaging material from the heated portions of the coated transfer sheet to the litho graphic surface of the lithographic master. Infrared radiation of an original to develop a heat pattern can be used in a number of other ways to develop imaging material on the master surface.

contemplated within the scope of this invention is the formation of an imaged lithographic master wherein the image formed on the lithographic surfiace is ink receptive and water repellent.

Common to all of the systems to which this invention is addressed is the exposure of the coated paper master to heat in one or more of the steps of image formation. Peculiar to the use of coated paper masters is the discovery that exposure to heat suflicient to fuse the developing material or effect transfer of imaging material from a coated transfer sheet causes curling, cockling, buckling or other distortions in the coated paper master. Characteristic also of such heated coated paper masters is the formation of blisters in the coating by reason of the inability for vapors released by the heat to escape through the coating.

The difficulties outlined above can be alleviated in part by double coating the paper base sheet to provide a series of back coats corresponding to the coatings applied onto the face of the sheet to form the master surface. Such double coating not only materially increases the cost of the plate, by reason of the additional amount of materials, the additional number of coating steps and the additional labor and equipment, but it also increases the thickness and stiffness of the master whereby it becomes less suitable for its intended use as a duplicating master for oflice copy work. Such double coating techniques operate more effectively to entrap vapors released upon heating such that the blistering problem still remains.

Attempts have been made to back coat the coated paper master in a manner to compensate for the imbalance introduced by the master coating on the face side of the plate but, as in the case of double coating, the desired balance is most difiicult to achieve and the back side coating continues to function as an additional barrier to the release of vapors whereby the blistering problem still remains.

Thus, it is an object of this invention to produce and to provide a method for producing coated paper duplieating masters which are relatively free of curling, buckling, cockling or the like distortion-s when exposed to heat and which minimize the formation of blisters in the coated surface. It is a related object to produce coated paper duplicating masters which are simple in construction; which embody a minimum amount of materials applied in a minimum number of coating steps, which retain their flexibility in use; which can be imaged in response to heat without resulting distortions of the plate and without formation of blisters in the coated surface, and which are capable of producing an imaged master of the lithographic type which lies flat and which has a desirably smooth reproducing surface.

These and other objects of this invention will hereinafter appear and, for purposes of illustration, but not of limitation, an embodiment of the invention is shown in the accompanying drawing, in which:

FIG. 1 is a perspective elevational view partially in section of a coated paper master embodying the features of this invention; and

FIG. 2 is a perspective elevational view, similar to that of FIG. 1, showing the coated paper master as an imaged lithographic plate.

In accordance With the practice of this invention, curling, bucking, cockling and other distortions and blistering resulting from heating of the coating paper duplicating master can be greatly alleviated to produce a substantially flat imaged plate when the coated paper duplicating master 10 is provided with a back coat 12 which imparts a degree of rigidity and which embodies a degree of porosity to permit the escape of moisture upon heating which moisture might otherwise cause the formation of blisters in the coated surfaces of the paper master by reason of the inability of the generated vapors otherwise to escape. The desired results are achieved by back coating the paper master with a composition formulated of a binder and colloidal silica as the principal and essential ingredients thereof.

As the binder, it is desirable to make use of casein, gelatin, algin, albumin and the like proteinaceous materials; polyvinyl alcohol, polyvinyl acetate, polyacrylates and polyalkylacrylates, butadiene-styrene copolymers, polyacrylic acid, starch and the like. As the colloidal silica, it is desirable to make use of a solution in which the colloidal silica has an average particle size within the range of 5 to 50 millimicrons and preferably within the range of 10 to 20 millimicrons. The ratio of colloidal silica to binder can be varied within the range of 0.1 to 10 parts by weight of colloidal silica to one part by weight of binder, depending somewhat upon the thickness and the character of the paper base sheet 14 and the thickness and character of the duplicating film or coating 16, which is provided thereon for receiving the image 18.

In formulation of the coating composition with proteinaceous binders, it is desirable to adjust the composition to the alkaline side for purposes of stabilization of the solution of colloidal silica and the proteinaceous binder. For this purpose, it is desirable to make use of ammonium hydroxide from which the ammonia can be volatilized off upon drying of the coating to produce an insoluble coating. For best practice, it is desirable to make use of an excess of ammonia in the solution to insure again-st coagulation or precipitation of either the colloidal silica or the proteinaceous binder from the coating composition.

Having described the basic concepts of back-coating whereby forces are inactivated which otherwise might cause blistering, curling, buckling, cockling and other distortions of the coated paper master upon heating, illustration will now be made of the practice of the invention in the back-coating of a coated paper lithographic master in which the lithographic coating 16 is formulated of casein pigmented with satin white. For illustration of a lithographic face coat of polyacrylate pigmented and insolubilized with zinc oxide, reference may be made to U.S. Patent No. 2,760,431.

SolutionA Parts by weight Casein 15.5 Zinc hydrate 0.6 Concentrated ammonium hydroxide 2.5 Water 81.4

- SolutionB Solution A 420 Hexamethylene tetramine solution 23 n-Butanol 3 Back-coating composition Solution B 448 Concentrated ammonium hydroxide 402 Colloidal silica (Ludox HS-E. I. du Pont30% solids) 324 The zinc hydrate employed in Solution A comprises a mixture of 24 parts by weight zinc sulphate, 5.4 parts by weight flake caustic soda (76%) and 70 part-s by weight of water. The above forms a slurry from which the zinc hydrate settles. The hexamethylene tetramine solution is prepared by blending equal volumes of concentrated ammonium hydroxide (28% NH Formalin (37% formaldehyde) and water.

The back-coating composition is applied by a conventional coating process, such as flow coating, roller coating or other conventional one side coating techniques onto the back side of the paper base sheet 14 and the coating is dried at an elevated temperature to set the coating. The composition is applied in an amount to provide a coating weight sufiicient to counter-act the face cu-rl depending upon the composition and character of the face coat, but in general it will be sufficient to provide a backcoat in coating weights within the range of 2 to pounds per 3,000 square feet of surface area.

Upon drying, the applied coating produces a layer 12 having capillary porosity to enable easy transmission of vapors and the layer 12 imparts a desired degree of stiffness. Thus the moisture vapor or other vapors generated during heating of the coated paper master in image formation finds easy and ready release through the back side coating 12 of the coated paper master. The stilTness imparted by the back coating operates further to resist distortions of the master by curling, buckling or cockling thereby to provide an imaged coated paper master which lies relatively flat and is free of blisters.

It will be apparent from the foregoing that there is provided a new and improved duplicating master which, by reason of the new and novel characteristics of the back-coating, is capable of being used in thermal processes for image development without wrinkling or buckling and without the formation of blisters in the imaged surface.

It will be understood that changes may be made in the details of construction, arrangement and operation without departing from the spirit of the invention, especially as defined in the following claims.

I claim:

1. A coated paper duplicating master comprising a paper base sheet having a face side and a back side, an image receiving coating on the face side onto which the image is to be formed and which is directly on the paper base sheet and only on the face side of the sheet and a separate single coating of the dried residue of colloidal silica and binder on the back side in which the single coating on the back side is characterized by microporous openings through which vapor-s can pass and by stiffness sufiicient to hold the master relatively flat and in which the materials are present in the back side coating in the ratio of 0.1 to 10 parts by weight of colloidal silica to one part by weight of binder.

2. A coated paper duplicating master as claimed in claim 1 in which the binder in the back side coating is casein.

3. A coated paper duplicating master as claimed in claim 1 in which the colloidal silica in the back side coating has an average particle size within the range of 5 to 50 millimicrons.

4. A coated paper duplicating master comp-rising a paper base sheet having a face side and a back side, an image receiving coating on the face side which is relatively impervious to vapor and which is directly on the base sheet and only on the face side of the sheet, a separate single coating of the dried residue of colloidal silica and a proteinaceous binder on the back side in which the single coating on the back side is free of any vapor impervious coating and in which the materials are present in the back side coating in the ratio of 0.1 to 10 parts by weight colloidal silica to one part by weight proteinaceous binder.

5. A coated paper lithographic master comprising a paper base sheet having a face side and a back side, a lithographic coating only on the face side, a single coating of the dried residue of colloidal silica and proteinaceous binder on the back side of the paper base sheet in which the coating is characterized by microporous openings through which vapors can pass, for stiffness sufficient to hold the master relatively fiat and in which the materials are present in the back side coating in the ratio of 0.1 to 10 parts by weight colloidal silica to one part by weight proteinaceous binder.

References Cited UNITED STATES PATENTS 2,760,431 8/1956 Beatty l0l-149.2 3,083,639 4/1963 Thurlow 10l--l49.2 3,220,346 11/1965 Strickler 101-1492 ROBERT E. PULFREY, Primary Examiner.

I. A. BELL, Assistant Examiner. 

1. A COATED PAPER DUPLICATING MASTER COMPRISING A PAPER BASE SHEET HAVING A FACE SIDE AND A BACK SIDE, AN IMAGE RECEIVING COATING ON THE FACE SIDE ONTO WHICH THE IMAGE IS TO BE FORMED AND WHICH IS DIRECTLY ON THE PAPER 